Our main goal is to elucidate the role of prolactin (PL) in the regulation of testicular function. We have previously shown that PL can increase testosterone (T) production in hypophysectomized animals treated with LH. We have also demonstrated that PL deficiency, caused by mutations or by treatment with ergot alkaloids, is associated with altered testicular function. It is proposed to examine the effects of treating hypophysectomized rats with PL, LH, FSH, or with various combinations of these hormones on the testicular response to a large dose of LH. This should provide new information on the involvement of PL in the regulation of testicular steroidogenesis before sexual maturation and in adult animals. It is also proposed to examine the effects of 2-Br-alpha-ergokryptine (Sandoz CB-154), an inhibitor of PL release, on T and dihydrotestosterone (DHT) levels in the peripheral blood, rete testis fluid (RTF), and testicular tissue of rats and mice. Finally, it is planned to study the effects of PL and CB-154 (given alone or in combinations with LH) on T levels in the peripheral plasma and RTF of rams fitted with chronic rete testis catheters. These experiments should be pertinent to the question of whether PL is necessary for normal function of the testis and whether the acute steroidogenic response to LH is modified by PL. We also propose to continue our work on T and DHT levels in the RTF of rats and in particular, on the correlation of androgen concentration in RTF and the maintenance of spermatogenesis under various experimental conditions.